Re: glibc very old
Vincent Lefevre <vincent@vinc17.net> writes:
>> So... these functions were made almost an order of magnitude slower
>> in the (overwhelmingly) common case, in order to handle rare and
>> exceptional cases...?
>
> This depends on the processor. You should get a processor that
> handles rounding-mode change in a better way (the slowdown should
> not be noticeable when you just run the program, without looking at
> the exact running time).
It's about 5 times slower on both phenom2 (AMD) and core2 (Intel)
cpus.... I dunno if these are unusual.
> But note that this could actually be slower with some processors:
> the processor already knows the rounding mode it is running under,
> so that if the rounding mode is not changed, the rounding-mode
> control instruction should be no slower than no-op!
Ok, I guess there's no really guaranteed way to make it fast, so
glibc's method (with arch-specific reimplementations for those cases
where it proves to be slow) it is reasonable enough ...
-miles
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